Computational Principles of Mobile Robotics

Sensing is a key requirement for any but the simplest mobile behavior. In order for Robot to be able to warn the crew of Lost in Space that there is danger ahead, it must be able to sense and reason about its sensor responses. Sensing is a critical component of the fundamental tasks of pose estimation – determining where the robot is in its environment; pose maintenance – maintaining an ongoing estimate of the robot's pose; and map construction – building a representation of the robot's environment. This need for sensing is illustrated in Figure 4.1, which shows a time-lapse photograph of a simple robot executing repeated motion in a carpeted lab. As the wheels slip, the true position of the robot deviates from its commanded position. Without external measurements of the outside world this deviation quickly results in the robot becoming “lost.”

In this chapter and the next we consider a range of sensing technologies. The sensors most strongly associated with mobility are those that measure the distance that the vehicle has moved (e.g., the distance the wheels have travelled along the ground), those that measure inertial changes, and those that measure external structure in the environment. For a robot to know where it is or how it got there, or to be able to reason about where it has gone, sensors and sensing algorithms are required.